The American eel: Tale of a champion migrator

The American eel spawns and hatches in the ocean waters of the Sargasso Sea, near Bermuda, about 2 million square miles of warm water in the North Atlantic.

Map of Sargasso Sea in relation to NYS, USFWS

The larvae of this snake-like fish drift with the currents for about a year to find homes throughout their huge range, from Greenland to Venezuela. Many eels migrate north and make it all the way to Lake Ontario.

A champion migrator if I’ve ever seen one.

Eels go through a very complicated maturation process that usually takes them from oceanic waters to freshwater and then back to the ocean for spawning. Some eels remain in saltwater or estuaries like the Chesapeake Bay their entire lives.

If you need a reason to conserve these amazing marathon swimmers, then here are some pretty unique behaviors to keep in mind. Eels can absorb oxygen through their skin and gills, allowing them to travel over land, particularly wet grass or mud (so cool!). Eels also can cover their entire bodies with a mucous layer, making them nearly impossible to capture by hand.

Historically, eels were abundant in Lake Ontario with over 1 million documented annually migrating upstream at the Moses-Saunders Hydropower Dam on the St. Lawrence River. In 2001, there was a huge drop to 944 migrants. Numbers have increased in the last decade, but are still below 50,000, leaving biologists looking for answers.

The extreme population decline may have been fueled by the 1970s demand for yellow and silver life stages of the American eel. Harvest can be especially detrimental because of the eel’s slow and complex maturation process, but the definite cause of the decline is still not clear.

American eels no longer have access to much of their historical habitat because dams and other obstructions in rivers block their migration and prevent them from accessing all available habitat. Localized population declines are also attributed to mortality in hydropower plant turbines, degradation of current habitat, and overharvest.

Addressing these threats to the American eel and its conservation is a multifaceted approach which includes research and monitoring to increase eel access to former habitat and understand the mysterious spawning migration, as well as reducing anthropogenic mortality.

Organizations including the U.S. Fish and Wildlife Service, Canadian Department of Fisheries and Oceans, New York State Department of Conservation, the Ontario Ministry of Natural Resources and Forests, the Quebec Ministry of Forests, Wildlife, and Parks, the New York Power Authority, Hydro Quebec, and Ontario Power Generation have targeted projects to develop methods to safely pass eel around hydro dams on large rivers.

Within New York State, our field office has partnered to track eel migration in the St. Lawrence River. Eels are tagged with acoustic tags in the Bay of Quinte (on the north shore of Lake Ontario). They then travel downstream along the St. Lawrence River and can be tracked with receivers located at the Iroquois Dam, about 80 miles downriver. That migration usually takes place in late summer or early fall when the eels are maturing from their yellow form to a beautifully elegant silver mature stage.

Documented eel movements at the Iroquois Dam in NYS, USFWS

In collaboration with other natural resource agencies, the Service continues to work to mitigate adverse impacts to eels. These measures are specified during the licensing or relicensing of hydropower projects by the Federal Energy Regulatory Commision and can include the addition of facilities like eel ladders to safely pass eels upstream, screens to keep eels out of turbines, passageways to guide them downstream, or shutting turbines down at night when silver eels migrate.

Service biologists collecting eel receivers on the St. Lawrence River, USFWS

Eel ladders, which are designed specifically for this species, allow eels to swim over barriers using an ascending ramp. Eel migration is monitored at various areas both upstream and downstream to help understand and optimize eel passage inland and to the ocean.

Other conservation actions include restrictions on eel harvest by the United States and by the federal and provincial governments in Canada.

The U.S. Fish and Wildlife Service continues to work with partners to better understand and conserve this remarkable species. The more informed we can be about the species around us, the better we are able to makes conscious choices to conserve and protect wildlife and the ecosystems in which we all live.

About this author

Sophie Trowbridge is the educational outreach coordinator for the New York Field Office in Cortland, NY. She is also a veterinarian and yoga teacher. Sophie is Interested in wildlife conservation medicine, One Health, and educational outreach. She enjoys using her veterinary knowledge to translate technical information and make it accessible to the public.

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